Most needed co-op zones/levels?

So I've come to a conclusion recently that I am not -- nor do I particularly want to be -- a guy that can hold up in the PVP game. That's nothing against people who enjoy it; I live in a world of laggy connections, slow thumbs, haphazard 'builds' and ADD-induced gear swapping, which sometimes compels me to go from greatswords and heavy armor to Oolacile magic and backstabbing in a single session. I'm not cut out for Souls PvP, and that's okay. I have a BLAST in co-op, and I enjoy the occasional impromptu invasion all the more, when it's not something I set out to do, and I'm working with a team. That, I can handle.

So, I'd like to set up a couple of toons (or maybe just one, Idunno) to really focus hardcore on co-op and PvE. Sunbro ****, I guess, basically. What's a good level range to shoot for, where I can reach the most people with the biggest need? Like I imagine basically Sen's Fortress and Anor Londo are probably the most-co-opped places, or.... idunno. I want to save the whole world. What soul level (and/or levels?) should I try to set up?

 
Oh! and this chart isn't limited to sunbros either.

Have a jolly good time.

PW, the depths, the township and royal wood (if you have them), and the archives (SL 75 might be a good level for that) are high traffic areas for co-op.